This invention relates to the extraction of ammonia and amines from aqueous solution using tetraphenylborate salts, in particular sodium tetraphenylborate.
Contaminants may enter the environment through discharge of industrial waste into a local water source, thereby imparting damaging and potentially devastating effects to the ecosystems which are dependent on the water source. Various methods have been proposed and implemented to reduce the level of contaminants present in water. However, such methods tend to be complicated and expensive, There is a need for alternative innovative technologies for removal of contaminants from waste water.
U.S. Pat. No. 4,695,387 (Berry et al.) discloses a process for continuous removal of ammonia from waste water using adsorption of ammonium ions to zeolite, and formation of ammonium phosphate from the adsorbed ammonium ions. The method employs a complex separation device having a plurality of chambers through which waste water must circulate. Although ammonium ion concentrations are reduced in waste water using this method, the removal of other nitrogen-containing contaminants from waste water is not addressed.
U.S. Pat. No. 5,641,413 (Momont et al., 1997) teaches removal of nitrogen from waste water having a high chemical oxygen demand. This method involves high temperature, high pressure oxidation and thermal denitrification to convert nitrogen-containing contaminants essentially to nitrogen gas. The process of U.S. Pat. No. 5,433,868 (Fassbender) employs a hydrothermal technique for removal of ammonia from water derived from sewage plant effluent. U.S. Pat. No. 5,407,655 (Sarritzu) discloses a process for recovery of pure (non-aqueous) ammonia from waste water through reaction with carbon dioxide, which also involves thermal decomposition, However, the high temperatures and pressures required in these processes necessitate the use of specialized tanks and equipment and thus tend to be expensive to conduct on a large scale.
U.S. Pat. No. 5,640,840 (Heitkamp et al., 1996) discloses a method for treatment of a liquid waste stream using microbial biodegradation whereby nitrogen-containing organic contaminants are ultimately converted to ammonia and carbon dioxide. The process involves flowing oxygenated waste water through a bed reactor supporting microbes capable of such biodegradation. This method requires the on-site presence of such a reactor, and recovery of purified water from the reactor may be a lengthy process.
Tetraphenylborates, particularly in the form of their alkali metal salts, are useful as counter ion components of cationic polymers in the field of non-linear optics (EP-A2-0 490 385), as polymerization initiators (U.S. Pat. No. 5,124,235), and as hydrophobic anionic functional groups dissolved in a polymeric matrix that is used in the separation of cesium and strontium from nuclear waste (U.S. Pat. No. 5,666,641). No work has heretofore been conducted to incorporate the use of tetraphenylborates in precipitation of ammonium ion or amines from waste water. All patents and publications referred to herein are expressly incorporated by reference.
An object of the invention is to provide a method of extracting ammonia and organic amines from water in an effective and environmentally acceptable manner.
One aspect of the invention provides a method for treatment of contaminated water to remove a nitrogen-containing species selected from ammonium ion and amines, which comprises contacting the water with sodium tetraphenylborate under acidic conditions, preferably weakly acidic conditions such as a pH value of between 3 and 7, and separating the treated water from the resultant precipitate of a salt of tetraphenylborate and the nitrogen-containing species.
Another aspect of the invention provides a method for treatment of contaminated water to remove a nitrogen-containing species selected from ammonium ion and amines (which hereinafter includes imines and any other species wherein the nitrogen atom will receive a proton), which comprises adjusting the pH value of the water to the acidic range, providing a polymer comprising a polymer backbone having a tetraphenylborate salt immobilized thereon, contacting the water with the polymer to dissociate the tetraphenylborate salt to tetraphenylborate ions and cations, whereby the nitrogen-containing species binds with the tetraphenylborate ions, and separating the treated water from the polymer having the nitrogen-containing species bound thereto. Preferably, the tetraphenylborate salt is a salt of Li+, Na+, K+, H+, Ca+2 or Mg+2. More preferably, Na+ is the cation.
A further aspect of the invention provides a polymer for removing a nitrogen-containing species selected from ammonium ion and amines from contaminated water, which polymer comprises a polymer backbone having a tetraphenylborate salt immobilized thereon in the form of dissociated tetraphenylborate ions and cations.
According to another aspect of the invention, there is provided an article for use in the removal of ammonium ion or amine from contaminated water, which comprises a containment vehicle having associated therewith a quantity of a polymer as defined above. The polymer may be, for example, in the form of cross linked beads or inert particles, e.g. silica, surface treated to be coated with tetraphenylborate groups, and the containment vehicle comprises, for example, a porous bag for the beads, a structure for supporting a bed of the beads, or a bed of sand having the beads entrained therein.
The invention also provides an article which comprises a means for introducing a solid or gaseous contaminated water source containing ammonia or amines, and converting said source to aqueous state.
The term contaminated water should be understood to encompass any water source containing ammonium ion or amine, and the invention is contemplated for use in the removal of ammonium ion or amine from any such water source. Thus, the method may be used, for instance to remove ammonium ion or amine from ground water, non-point run-off water, mine infiltration water, industrial effluent, and any other type of contaminated water or waste water.
In the case where ammonium ions or amines may be air-borne, or found in any other gaseous medium, such compounds may be captured and converted from the gaseous medium to an aqueous medium and removed according to the invention. An example of such an application is in the case of volatile ammonia and amines which arise from animal waste in an environment such as an enclosed chicken barn. Additionally, ammonium ion or amines derived from a solid source, such as animal waste, could be solubilized in water and removed therefrom according to the invention.
The invention may also be used as a pre-concentration method for extracting and concentrating small traces of amines or ammonium ion before analysis therefor. The invention can thus be employed for test methods to quantify amines or ammonium ion. The invention may be used for analysis of street-drug mixtures, most of which are amines, whereby the amine component can be sequestered from an admixture. The invention may also be used for recovery of any amine which can be converted into a quaternary (charged) nitrogen system. Even (CH3)4N+ and related species having no Nxe2x80x94H bond can be extracted using the method of the invention.
Amines which form insoluble salts with the tetraphenylborate anion and can be removed from aqueous media according to the invention include aliphatic amines such as alkylamines including methylamine, ethylamine, and propylamine, as well as guanidine and biguanidine; diamines of the formula NH2 (CH2)nNH2 where n is an integer, such as ethylene diamine and propylene diamine; aromatic amines such as aniline and benzylamine; heterocyclic amines such as optionally substituted pyridine, pyramidine and pyrazine; polycyclic amines such as tropane and 1,4-diazabicyclo [2.2.2] octane (DABCOH), and also caffeine and nicotine.
The method is based on the formation of ammonium tetraphenylborate (NH4BPh4), a salt which is very insoluble in water. When a slightly acidic aqueous solution of ammonia or an amine is added to an aqueous solution of sodium tetraphenylborate, an immediate, thick, white precipitate is formed. This precipitate of NH4BPh4 is non-gelatinous, powdery but granular and is easily filtered. While NH4BPh4 is insoluble in water, it is soluble in acetone and acetonitrile. It can be recrystallised from acetone/water mixtures (or from acetonitrile) and the crystals appear to be stable indefinitely, Preferred pH values for the aqueous solution range from about 3 to 7, particularly from about 4 to 6.
The nitrogen-containing species in the contaminated water is normally in the form of a soluble inorganic or organic ammonium salt or an amine and the method of the invention is particularly suited to the treatment of waste water streams, such as water polluted with industrial effluent or acid rain. Mine infiltration water also contains a high ammonia concentration when derived from prehistoric sources. Removal of ammonia is required prior to release of mine infiltration water into the environment.
Simple, apparently uncomplicated, salts of ammonia are rarely insoluble. When the crystal structure of NH4BPh4 was completely determined (Cand J Chem 58 (1980) 1355), it was shown to be a most extraordinary system, The NH4+ and BPh4xe2x88x92 ions stack in columns, alternating . . . NH4+ . . . BPh4xe2x88x92 . . . NH4+ . . . BPh4xe2x88x92 . . . with the NH4 ions trapped in a cage produced with a pair of phenyl groups from each of the two adjacent BPh4xe2x88x92 ions.
In itself this is not unusual, but within the columns the NH4+ ions form four hydrogen bonds to the planes of the four phenyl rings in the surrounding cage. The short contact Nxe2x80x94H . . . Ph, the careful IR work in the paper cited above and elegant thermodynamic measurements by L. Stavely in Oxford in the 1960""s (ref in Cand J. Chem paper) makes it clear that this Nxe2x80x94H . . . Ph interaction is a significant hydrogen bond. The favorable lattice energy for NH4BPh4, which is the source of its insolubility, comes then not only from a most favorable ion packing but also has a contribution from these hydrogen bonds.
The contribution from the hydrogen bonds is crucial and instrumental in the unique properties of NH4BPh4. Our subsequent X-ray structure determinations have shown that the Nxe2x80x94H . . . Ph hydrogen bond (or a variant thereof is present in every case where the organo-ammonium salt has an Nxe2x80x94H bond while the very favorable cage arrangement has often been seriously degraded. We have ascertained that the charge interaction (cation/anion) is necessary as is the Nxe2x80x94H . . . Ph interaction, but the symmetrical cage is less vital.
In order to verify the efficiency of the method of the invention, model systems were examined with NH4+ ions present in solution in concentrations ranging from 10 to 200 ppm. These solutions were treated with stoichiormetric quantities of NaBPh4, dissolved in water and then one additional drop of NaBPh4 solution was added to ensure the presence of NaBPh4 in excess. The solutions were allowed to settle and the residual ammonium ion concentration in the supematant was estimated by (a) Nessler""s reagent, and (b) electrospray mass spectrometry seeking to detect the chloramine ion.
The Nessler""s reagent studies gave consistent readings of a total residual NH4+ concentration in the supernatant liquid ranging between 3 and 5 ppm. The mass spectrometric measurements confirmed these results since no ammonium ions were detected in the supematant liquid.
Thus, we concluded that NH4BPh4 is so insoluble a material that when equimolar quantities of NH4+ and BPh4xe2x88x92 ions are mixed in solution, the concentration of residual NH4xe2x88x92; ion (ions not complexed with BPh4xe2x88x92) is very low, probably below 1 ppm.
The supematant liquid was examined by mass spectrometry over a period of several days. The boron species present in solution were easily identified by the natural isotopic abundance of boron. Over a period of a week, the levels of boron species in water stayed unchanged, and no new species were observed to emerge. These results confirm that the NH4BPh4 solid is stable over an extended period of time when left in contact with water. These experiments were conducted at two representative temperatures, 25 and 35xc2x0 C. and both experiments showed the same stability.
Following extraction of the ammonium ion or amine, the NaBPh4 can be regenerated as outlined below.
The method depends on the fact that although NaBPh4 is soluble in water and KBPh4 is insoluble, KBPh4 is isomorphous with NH4BPh4. This is not surprising since NH4+ and K+ occupy roughly tile same space in a crystal and are often mutually exchangeable in crystal structures.
While the two structures are isomorphous, the KBPh4 system does not have the added advantage of four Nxe2x80x94H . . . Ph hydrogen bonds. Thus, when KBPh4 is stirred in a solution containing the NH4+ ion, the equilibrium:
KBPh4(solid)+NH4+(soln)⇄NH4BPh4(solid)+K+(soln)
is strongly displaced to the right, that is towards the formation of NH4BPh4(solid).
The process involves stiring excess KBPh4 in the NH4+ solution until the concentration [NH4+] starts to rise. The xe2x80x9cspentxe2x80x9d KBPh4 is then filtered off. The spent KBPh4 is then stirred with a mild base such as K2CO3, and the ammonia and amines are released, since once the ammonia or amine is neutralized it loses its charge and the main component of the lattice energy of the NH4BPh4 salt is also lost. This simply reverses the equilibrium equation given above by the removal of the NH4+(soln) species from the system.
KBPh4 is reformed by this process and the regenerated KBPh4 can then be filtered and re-used. The filtrate contains the amines (and ammonia dissolved as NH3) in solution. Acidification of the filtrate, followed by evaporation produces the solid ammonia and amine salts which can be collected and separated by differential vacuum sublimation.
In an alternative embodiment, sufficient Na2CO3 solution is added to the separated NH4BPh4 to neutralise all the ammonia and amines. NaBPh4 remains in solution and the ammonia and amines can be removed by distillation (reduced pressure distillation to preserve the BPh4xe2x88x92 ion). The NaBPh4 already in solution is then available for re-use.
Another aspect of the invention relates to the use of functionalized polymers or surface modified particles for separation of ammonium ions and amine salts from water. In the former case this involves the use of a polymer which incorporates the BPh4xe2x88x92 moiety. Such a polymer is preferably synthesized in the form of beads that consist of a lightly cross-linked network onto which BPh4xe2x88x92 groups are attached. In the latter case, a suitable material such as particles of silica, alumina or titania, for example, are subjected to a surface modification so as to chemically attach BPh4xe2x88x92 groups. Since it is important to maximize the interactions of the ammonium species with the BPh4xe2x88x92 groups, it is necessary to employ a polymeric backbone with suitable hydrophobicity. Many backbones may be used ranging from somewhat hydrophobic polystyrene to the more hydrophilic polyethers.
Preferred polymer backbones include polystyrenes, polyethers and polyacrylamides, as well as silica, which is an inorganic polymer. Further copolymers including these and other hydrophobic and hydrophilic monomers may also be used. Particularly advantageous polymers include a porous, lightly cross-linked polystyrene resin that is functionalized to contain the tetraphenylborate functional group, and a more hydrophilic polyether polymer system also functionalized to contain the desired functional group. In addition, silica particles may be used as the support (or polymer) and may be surface-coated so as to feature the desired functional group as the active entity.
In all three cases, the tetraphenylborate functional group is preferably neutralized as the sodium salt. The binding of the ammonium species occurs by the displacement of the sodium ions, as in normal ion exchange processes. Alternatively, the other suitable cations may be used such as LI+, K+, H+, Ca+2 or Mg+2. The cations bound to the tetraphenylborate ion are herein referred to generally as M. Regeneration of the materials can be accomplished by washing with concentrated Na2CO3(NaCl) solution, sodium bicarbonate solution or carbonic acid, for example, using methods known to those skilled in the art.
The phenyl groups of the tetraphenylborate group can optionally be substituted in para position by halo, e.g. fluoro or chloro, lower alkyl, e.g. methyl, or lower alkoxy, e.g. methoxy.
The following embodiments are presented as detailed examples of polymers for use in the invention.
All embodiments contain the active binding unit, tetraphenylborate, attached directly or indirectly to a polymeric backbone as shown schematically in formula (I) below. The tetraphenylborate moieties may be present as surface modifying agents or incorporated into a cross-linked resin. In formula (I), the tether (R1) may be a lower alkyl group or simply a carbon-to-carbon bond, and M is a cation. 
In a first embodiment, a polymer comprises cross-linked, functionazed polystyrene to which tetaphenylborate is tethered, and has the general formula: 
wherein x refers to a styrene comonomer and is from 0 to 50 mol %, z refers to a cross linking agent and is from 1 to 10 mol %, y refers to a comonomer having the tethered tetraphenylborate group and is [100xe2x88x92(x+z)] mol %, and R2 is a carbon-to-carbon bond or C1 to C6 alkyl, and M is a cation.
In a second embodiment, a polymer comprises a cross-linked polyether backbone with tetraphenylborate tethered thereto, and has the following repeating unit: 
R3 is C1-C6 alkyl
R4 is H or C1-C6 alkyl,
R5 is a carbon-to-carbon or C1-C6 alkyl, and M is a cation.
More specifically, according to the second embodiment, a polymer comprises a polyether backbone with tetraphenylborate tethered thereto, and has repeating units as follows: 
wherein:
each R3 independently represents C1-C6 alkyl,
R4 is H or C1-C6 alkyl,
R5 is a carbon-to-carbon bond or C1-C6 alkyl,
R6 is phenyl or C1-C6 alkyl
R7 is phenyl C1-C6 alkyl or cross linking unit,
M is a cation,
m is 0-50 mol % (comonomer),
p is 1 to 10 mol % (cross linking agent), and
n is [100xe2x88x92(m+p)] mol % (comonomer having the tethered tetraphenylborate group).
In a third embodiment a polymer comprises a silica backbone having pendant tetraphenylborate groups as shown below: 
wherein R8 is a carbon-to-carbon bond or C1-C6 alkyl, and each R9 independently represents C1-C6 alkyl or H, and M is a cation.